can we cool it please, I think all points have been made well enough by now.
If we are talking rigol scopes (DS1xxxE/D series) the maximum that you can measure is 30V, 300V with a 10X probe and therefore 3000V with a 100X probe.
The 300V figure on the front panel is part of the CAT rating and means that if you give it a spike of more than 300V it will probably deservedly die as it is 10X the measuring capacity.